A wonderful manifestation of cable channels rushing to make brilliant, challenging television without the shackles of ratings needs or, in some cases, advertiser worries, is that ambition run amok often leads to great things. Like complicated, intelligent, richly crafted series. Like "Breaking Bad." Or "Dexter." Or "Mad Men."

But big risks demand an audience that goes along for the ride, an audience that understands that what it's about to witness won't be easily digested or even pigeonholed. It won't have all the familiar elements that reassure people and give them courage to keep watching. Sometimes it's hard to understand or interpret the early stages of ambition. Our knee-jerk instinct is to sometimes ignore it, perhaps even mock it.

But if a succession of superb series coming from cable channels has taught viewers anything, it's to be patient, to give writers the benefit of the doubt. On Sunday, Showtime - a pay-cable channel that has never blinked in the face of audacity - premieres the much-anticipated series "United States of Tara," starring Toni Collette as a wife and mother suffering from multiple personalities. The medical community no longer calls it that, preferring the term dissociative identity disorder, or DID. In any case, the Tara in question is four distinct people in one body.

"United States of Tara" brims with great acting, humor and a disarming amount of tenderness. It's one of those series with overabundant potential and early hints of provocative brilliance, but it may take a while to truly arrive.

Executive-produced by Steven Spielberg and created and written by Diablo Cody ("Juno") - with many of the episodes directed by Craig Gillespie, who tapped into a similar vein with his film "Lars and the Real Girl" - "United States of Tara" approaches mental illness with humor and compassion. The series is a tour de force for Collette but also a wonderfully nuanced portrait of marriage and family, with all the satirical edge you might expect from Cody.

Family matters

The immediate challenges of "United States of Tara" are clear from the first episode, when Tara Gregson (Collette) is suddenly transformed into T, a wild-child teenager who smokes pot, likes sex and has a foul mouth. Tara's family just goes with it. Husband Max (John Corbett) has been married to Tara for 17 years and is nearly saintly in his understanding of her condition. Daughter Kate (Brie Larson) is less so; she's an interesting mix of sexually active, rebellious teen daughter and mature, go-with-it family member.

Marshall (Keir Gilchrist), their possibly gay, sensitive, intelligent freshman son, has the compassion of his father but also less of the Zen, it'll-all-work-out part of Dad. Marshall worries about Tara and is very protective of her. Together they endure the "alters" - alternative personalities - who pop up in the house (and who have become familiar in the small town where they live).

Why, viewers are likely to ask, is the Gregson family being so relaxed about Mom's problem? The alters seem to pop up with annoying frequency. Buck is a trucker-hat-wearing, beer-chugging, homophobic, gun-loving Vietnam vet - and, yes, a man. Alice is part Stepford wife and part God-fearing, Martha Stewart-esque danger mom.

The arrival of T, Buck or Alice would crater most families - and we'll learn later that the Gregsons do struggle - but mostly Tara is blessed by a family that opts to forgive rather than freak. The least understanding person is Tara's sister, Charmaine (Rosemarie DeWitt from "Rachel Getting Married"), who believes that Tara doesn't have a real disease and who also is jealous of all the attention it brings her.

Tara has quit her meds. Stress triggers the appearance of her alters. But "United States of Tara" should have made that clear earlier and more clearly. And the bigger issue - why Tara stops taking her meds - remains murky.

Into the wild

Yes, Tara, an artist at heart who less glamorously paints murals for a living, feels she can't work, sleep or emotionally connect with her family when she's taking her medication. But she's also apparently hoping that studying these alters in the wild, if you will, might provide some understanding of why they exist (even though studies suggest that severe childhood trauma is the cause).

We can guess that Tara is looking to make herself whole by understanding her multiples. She meticulously jots down notes culled from the family after one of the alters has come and gone, since she can't remember the experience. After four episodes, it's not quite clear how sane that approach really is or even whether it has medical merit. And yet, the series uses a DID expert, Dr. Richard P. Kluft, as a consultant, and the producers (including Cody) have all studied this very real disorder.

Kluft said in a statement that the series "takes an important step toward respecting, humanizing and de-stigmatizing DID and those who suffer from it, usually in painful isolation."

Ambition and patience

This all speaks to the ambition in "United States of Tara" and the patience that viewers will need (or won't, depending on how skeptical you are of motivation and plausibility). What the series has going for it, however, grows clearer with each episode. The Gregsons aren't "normal" as far as TV families go, and that's a good thing. Even though the series is built around Tara's illness, it's very much a series about family. And even though Collette is given a dream role, it's a testament to Cody's broader view in the writing that the other actors really shine.

In fact, the casting is superb. As Max, Corbett's low-key vibe is the perfect counterpart to Collette's freewheeling riffs. As the outwardly disaffected and sassy daughter, Kate, Larson is able to find nuance - she's angry at her mom but loving as well. She's not too pouty and snarky to participate in ballet at school. Gilchrist is a real find as Marshall, whose interest in classic films and jazz can't hide his inherent geekiness.

It's also refreshing that Tara and Max are allowing him to discover on his own whether he's gay or not (Kate is convinced, of course). And DeWitt - who's a revelation in everything she's been in - deftly brings out the sibling-rivalry element in Charmaine without using that as her sole card. Patton Oswalt has a recurring role as Max's co-worker.

Showtime knows how to shepherd ambition, and so the bet here is that "United States of Tara," despite some early reservations that viewers might have, will continue to evolve and deliver on its enormous potential. This is a series that's tackling a difficult subject with humor and warmth, but also from a fresher angle. Who knows, ultimately, how successful the series will be after the 12-episode season, but for fans of quality television, the reward is always in the trying.

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